Spherical Bearing Arrangements

ABSTRACT

A method of manufacturing a spherical bearing arrangement, the method comprising: providing a ball and a cast bearing housing; elevating the ductility of the cast bearing housing; and swaging the housing onto the ball whilst the ductility is elevated, the ductility lowering after swaging.

FIELD OF THE INVENTION

The present invention relates to a spherical bearing arrangement and amethod of manufacture thereof.

BACKGROUND AND DESCRIPTION OF RELATED ART

A spherical bearing arrangement comprises a spherical ball mounted in ahousing. The ball is mounted in the housing such that it can rotatefreely in all directions but without allowing any (or at least veryminimal) translational movement relative to the housing. The ball issometimes mounted in the housing such that there is a predeterminedtorque or clearance between the ball and housing. Such spherical bearingarrangements are well known and find application in the aerospace andautomotive industries.

The preferred method of mounting the ball in the housing is to swage(i.e. deform) at least a portion of the housing onto and around the ballto entrap it therein—thereby preventing relative translational movement.After swaging, the outer surface of the ball and the inner surface ofthe housing conform closely to one another so as to form a bearinginterface—thereby affording relative rotational movement. To ensureclose conformity of the two surfaces post-swaging (i.e. after swaging),a machining step is sometimes carried out on the inner surface of thehousing pre-swaging (i.e. before swaging).

In order for the housing to be effectively swaged onto the ball, thematerial from which the housing is made must be sufficiently ductile towithstand the deformation caused by the swaging process. It is widelyaccepted, therefore, that housings having a high ductility are the mostsuitable for the swaging process. By high ductility is meant thatductility is in the order of 10% and greater.

Prior art bearing housings are manufactured from a stock ‘billet’ ofmetal. A billet of metal simply comprises a large block of a cast metal(or a mixture of metals, according to the customer's requirement). Thebillets are delivered to the bearing housing manufacturer and are thenmachined (e.g. cut, milled, drilled etc) to create the bearing housingto swage onto the ball. It will be appreciated that a large volume ofmaterial is removed in this process (sometimes >80%).

However, due to the nature of the casting process, the cast billets tendto have a large grain size which contributes to their having a lowductility. By low ductility is meant that ductility is in the region ofless than 10%. Furthermore, the grain structure of cast materials is notuniform, which acts further to reduce the ductility thereof.

When a swaging operation is performed on cast articles having such lowductility, the articles tend to crack and fail; at the very least, theswaging is not performed to a satisfactory, repeatable, level. In thecase where the article is a housing for a spherical bearing arrangement,it is a strict requirement that certain characteristics of the resultantbearing arrangement (e.g. torque, clearance etc.) are maintained withina narrow, predetermined range. Any manufactured bearing arrangementshaving characteristics falling outside of these ranges need to bere-worked or even scrapped, at high financial cost.

Accordingly, to avoid cracking or otherwise mechanical failure of thebearing housing during the swaging process—which can result in thecharacteristics of the bearing falling outside of the predeterminedrange(s)—it is accepted that the cast billet must first be mechanicallyworked in order to increase its ductility to a suitable level whereswaging can be performed with satisfactory, repeatable, results.

Such mechanical working of the billet material involves at least oneprocess of, for example, forging, extruding and rolling. Following suchprocesses having been carried out, the resultant worked material has asmall equiaxed grain structure, which acts to increase the ductility ofmaterial to a level that is sufficient to allow for swaging to beeffectively carried out, without the risk of cracking or mechanicalfailure occuring.

Furthermore, to ensure a suitable level of ductility of the workedmaterial is achieved, only billet metals and materials having arelatively high initial ductility are considered. Examples of suchmetals are steel and copper/bronze. Indeed, even if materials having alow initial ductility are mechanically worked in an attempt to increasethe ductility thereof, these operations still do not result in amaterial having a ductility suitable for swaging. Materials having a lowinitial ductility, therefore, are simply not considered as beingsuitable for mechanically working to elevate ductility or for swagingoperations per se.

It will be appreciated that the separate “mechanical working” operationsof forging, extruding, rolling and/or machining etc add many additionalsteps to the manufacturing process over that of the initial casting andthe later machining to form the bearing housing ready for swaging. Inaddition, materials having a high ductility such as steel andcopper/bronze are expensive in comparison to other materials having arelatively lower ductility. However, such methods and materials havehitherto been accepted as necessary in order to manufacture a housinghaving the desired ductility to enable the housing to be effectivelyswaged around and onto the ball without the risk of cracking ormechanical failure.

SUMMARY OF THE INVENTION

It is an object of the present invention to seek to overcome at leastsome of the aforementioned problems.

Accordingly, one aspect of the present invention provides a method ofmanufacturing a spherical bearing arrangement, the method comprising:providing a ball and a cast bearing housing; elevating the ductility ofthe cast bearing housing; and swaging the housing onto the ball whilstthe ductility is elevated, the ductility lowering after swaging.

Preferably, the method further comprises: performing at least onemachining operation on the cast housing prior to swaging thereof.

Advantageously, the method further comprises: performing at least onemachining operation on the resultant spherical bearing arrangement.

Conveniently, the elevation of the ductility is performed by heating thehousing.

Preferably, the ductility is lowered after swaging by cooling thehousing.

Advantageously, the ductility of the housing prior to elevation is lessthan 10%.

Conveniently, the ductility of the housing prior to elevation is lessthan or equal to substantially 9%.

Preferably, the ductility of the housing prior to elevation is less thanor equal to substantially 8%.

More advantageously, the ductility of the housing prior to elevation isless than or equal to substantially 7%.

Conveniently, the elevated ductility is at least 10%.

Preferably, the elevated ductility is at least substantially 11%.

Advantageously, the elevated ductility is at least substantially 12%.

Conveniently, the elevation of the ductility is performed by providingthe housing at a predetermined temperature.

Preferably, the predetermined temperature is at least substantially 80°C.

Advantageously, the predetermined temperature is at least substantially90° C.

Conveniently, the predetermined temperature is at least substantially100° C.

More preferably, the predetermined temperature is at least substantially110° C.

More advantageously, the predetermined temperature is at leastsubstantially 120° C.

Conveniently, the lowered ductility of the housing is at leastsubstantially equal to the ductility of the housing before elevation.

Preferably, the lowered ductility of the housing is substantiallygreater than the ductility of the housing before the elevation.

Advantageously, the material of the bearing housing comprises metal.

Conveniently, the metal is zinc or zinc alloy.

Another aspect of the present invention provides a spherical bearingarrangement, comprising a cast bearing housing swaged onto a ball,wherein the ductility of the housing is elevated during swaging andlowered after swaging.

Yet another aspect of the present invention provides a rod end bearingcomprising the spherical bearing arrangement of the present invention.

In any event, the present invention provides a method of manufacturing aspherical bearing arrangement or a spherical bearing arrangement asdefined in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only,with reference to the accompanying figures, in which:

FIG. 1 is a perspective view of a spherical bearing arrangementmanufactured in accordance with a method embodying the presentinvention; and

FIG. 2 is a cross-sectional view of the spherical bearing arrangement ofFIG. 1 along line A-A;

FIG. 3 is a cross-sectional view of a bearing housing prior to swagingused in a method embodying the present invention;

FIG. 4 is a cross-sectional view of another bearing housing prior toswaging used in a method embodying the present invention;

FIG. 5 is a perspective view of another bearing housing prior to swagingused in a method embodying the present invention; and

FIG. 6 is a cross-sectional view of the bearing housing of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 2 show a spherical bearing arrangement 1, comprising: abearing housing 2; and a ball 3 mounted therein. The bearing housing 2is substantially annular and comprises a cylindrical outer surface 4with two axial end faces 5 and an inner surface 6 comprising a sphericalhousing bearing surface. The bearing housing 2 further has a centralaxis 7. The ball 3 is substantially spherical in shape, with a sphericalbearing surface 8 conforming to the housing bearing surface 6 such thatthe bearing surfaces 6,8 are in sliding contact with one another so asto form a bearing interface. In this example, the ball 3 has an axialend face 9 at either end of a bore 10 passing through the ball 3. Thebore 10 has a central axis 11 passing therethrough and, in use, a shaftis often inserted in the bore 10 (not shown).

FIG. 3 shows a housing 12 prior to being swaged onto the ball 3, wherelike reference numerals are used to denote like features. The housing 12comprises a substantially cylindrical outer surface 13, a substantiallycylindrical inner surface 14 and two axial end faces 5. Thesubstantially cylindrical inner surface 14 defines a bore 15 of thehousing 12. Preferably, the diameter of the bore 15 is greater than thediameter of the ball 3. Accordingly, the ball can be inserted into thebore 15 of the housing 12. Alternatively, the diameter of the bore 14may be equal to or very slightly less than the diameter of the ball 3 soas to provide a slight interference fit.

In a method of manufacturing a spherical bearing arrangement embodyingthe present invention, the housing 12 is provided with a ball 3 insertedtherein. At least a portion of the housing 12 is then swaged around andonto the ball 3 so as to entrap the ball 3 in the housing 12. Theresultant spherical bearing arrangement 1 is shown in FIGS. 1 and 2.After swaging, the inner surface 6 of the bearing housing 2 is insliding relationship with the outer surface 8 of the ball 3, so as toform a bearing interface. Following swaging, the ball 3 is able torotate in all directions with respect to the housing 2 but relativetranslational movement is substantially prevented.

It will be appreciated that immediately following the swaging of thehousing 12 of FIG. 3 onto the ball 3, the outer surface 13 thereof willbe substantially convex. It will be noted, however, that the outersurface 4 of the resultant bearing housing 2 shown in FIG. 2 iscylindrical. This is because there is preferably a machining operationperformed on the outer surface 13 of the housing 12 after swaging, sothat the outer surface 4 of the housing 2 is cylindrical—which aidsinsertion of the resultant bearing into a rod end for example.

In a method embodying the present invention, a cast bearing housing isprovided. By cast bearing housing is meant a cast item in the shape of abearing housing. Conveniently, the cast housing substantially takes theform of the housing 12 shown in FIG. 3. To cast the housing, moltenmetal is poured into two mated mould portions, each mould portiondefining a female profile of one half of the bearing housing. Many othertypes of moulds and methods of casting are well known in the art and areaccordingly encompassed by the invention. Other examples are: lost wax,sand casting, hot chamber die casting, cold chamber casting and spincasting.

Preferably, following the casting of the bearing housing 12, onlyminimal machining operations need be carried out on the housing 12before it is ready for swaging, for example fettling or de-burring ofsurfaces of the housing. Additionally, it will be appreciated that anyrisers attached to the cast housing 12 must be removed and thesurrounding surface smoothed. Conveniently, any such machiningoperations are purely cosmetic and are not performed so as todrastically alter the general shape of the cast housing 12. As a result,a bearing housing 12 cast in a method embodying the present inventionsubstantially resembles that shown in FIG. 3.

Due to the nature of the casting process, the ductility of the casthousing 12 is low, due at least in part to the large grain size andnon-uniform grain structure thereof. By low ductility is meant aductility of less than 1O%. As a result, the cast housing 12 is notsufficiently ductile for it to be swaged immediately onto the ball 3 toform a spherical bearing arrangement 1. A method embodying the presentinvention provides for the elevation of the ductility of the castbearing housing 12 whilst the housing 12 is being swaged onto the ball3.

Conveniently, a method of manufacturing a spherical bearing arrangementembodying the present invention comprises: providing a ball and a castbearing housing, the bearing housing having a first ductility; elevatingthe ductility of the cast bearing housing to a second ductility; andswaging the housing onto the ball whilst the ductility is elevated (i.e.at the second ductility), the ductility lowering to a third ductilityafter swaging. Preferably, the third ductility is equal to the firstductility. Alternatively, the third ductility may be higher or lowerthan the first ductility. Preferably, the ductility of the housing 12prior to elevation is less than 10%. Conveniently, the ductility of thehousing 12 prior to elevation is less than or equal to substantially 9%.Advantageously. the ductility of the housing prior to elevation is lessthan or equal to substantially 8%. Most preferably, the ductility of thehousing prior to elevation is less than or equal to substantially 7%.

In a method embodying the present invention, the bearing housing 12 ispreferably heated, which acts to elevate the ductility of the housing12. Preferably, the elevated ductility is at least 10%. Conveniently, itis at least substantially 11%, Advantageously, it is at leastsubstantially 12%. Most preferably, the elevated ductility is such thatit permits the housing 12 to be swaged onto the ball 3 without the risk(or at least significantly reducing the risk) of the housing 12 crackingor otherwise mechanically failing. Methods embodying the presentinvention allow swaging of cast bearing housings 12 to be performed withsatisfactory, repeatable, results. As a further consequence, the numberof spherical bearing arrangements being scrapped for havingcharacteristics outside of the very narrow tolerances is significantlyreduced, saving costs.

Such an elevation in the ductility is brought about, in one embodiment,by the heating of the housing 12 altering the grain structure of thehousing 12. Conveniently, the housing 12 is not heated to a level wherethe material of the housing 12 exhibits superplastic behaviour.Accordingly, when the housing 12 is cooled after the elevation, thestructure of the material substantially returns to the structure priorto elevation. Preferably, when the housing 2 is cooled, the ductility issubstantially equal to that before elevation occurred. Alternatively,the ductility of the housing 2 after cooling may be slightly higher orlower than the ductility of the housing 12 prior to elevation. In anyevent, methods embodying the present invention ensure that the ductilityis elevated from its initial level throughout the swaging process.

With spherical bearing arrangements according to the prior art, thematerial from which the bearing housing is machined is mechanicallyworked so to increase the ductility thereof to a level sufficient toallow swaging. As a result of such mechanical working, the raisedductility of the material is often permanent. At the very least, only aminimal decrease in ductility is experienced immediately following themechanical working processes having been completed. The increasedductility of such prior art housings is substantially stable and ismaintained when the housing is substantially at room temperature.

Thus, with bearing housings according to the prior art, the ductility ofthe housing after swaging will be at a level sufficient for furtherswaging to be effectively and reliably performed, for example aductility in excess of 10%.

The housing of a spherical bearing arrangement manufactured according tothe present invention, on the other hand, preferably has a level ofductility after swaging which is lower than that required to effectivelyand reliably perform further swaging. As a result, spherical bearingarrangements manufactured according to a method embodying the presentinvention benefit from higher yield strength, higher fatigue strengthand higher compressive yield strength, as well as greater hardness, whencompared to a spherical bearing arrangement manufactured in accordancewith a method not embodying the present invention. The bearing willtherefore be able to more readily resist deformation in use due to thearrangement being subject to extreme axial forces and the like.

Preferably, the elevation of ductility in methods embodying the presentinvention is only temporary. By temporary is meant that the duration ofthe elevated ductility is such that it is sufficient for the purposes ofthe swaging operation to be performed. This temporary elevation alsoensures that no long lasting changes are encountered in the grainstructure or size of the material of the housing. Preferably, thehousing is actively cooled after elevation by, for example, a coolant orrefrigerant system. In another embodiment, the housing may be passivelycooled by exposure simply to the ambient temperature.

Preferably, the material of the housing is zinc or zinc alloy. Such ametal is especially convenient in that it is cheap, in relation to, forexample, steel and copper/bronze, and it is suitable for casting. Zincor zinc alloy is traditionally not suitable for swaging. By practisingthe method of the invention on a casting material which is otherwiseunsuitable for swaging, the casting material can then be swaged.

FIG. 4 shows another form of cast bearing housing manufactured accordingto a method embodying the present invention. In this figure, the housing16 has a substantially convex outer surface and a substantially concaveinner surface. Such a shape of bearing housing is convenient during theswaging process in ensuring that the respective bearing surfaces of theball and housing conform closely and uniformly with one another, toavoid pinching and the like. Of course, the bearing housing of aspherical bearing arrangement manufactured according to a methodembodying the present invention may take any form and the exemplaryarrangements shown in FIGS. 3 and 4 are not to be seen as limiting.

The embodiments shown in FIGS. 1 to 4 relate to a spherical bearingarrangement wherein both axial ends 5 of the housing 2, 12, 16 areswaged onto the ball 3. Another embodiment of a housing 17 on which themethod of the present invention can be practised is shown in FIGS. 5 and6. The bearing housing 17 comprises an inner spherical bearing surface18 (loosely resembling a cup) for receiving the ball 3. Most preferably,the inner spherical bearing surface 18 substantially conforms to thespherical outer surface 8 of the ball 3 to be inserted therein. Thehousing 17 further comprises an annular wall 19 upstanding and extendingperpendicularly away from the base 20 thereof. The inner surface 21 ofthe annular wall 19 is substantially cylindrical. The housing 17 is acast part and preferably at least one machining operation is performedafter casting to ensure that the inner spherical surface 18 conformsclosely to the spherical surface 8 of the ball 3 to be inserted therein.The base 20 of the housing 17 preferably includes a flange 22 for fixingthe housing 17 to another object.

When the housing 17 of FIGS. 5 and 6 is used in a method embodying thepresent invention, only the annular wall 19 need by swaged over the ball3. In any event, practising a method embodying the present invention onthe housing 17 conveniently allows for the housing to be more readilyswaged onto a ball 3 without cracking or mechanical failure. It will beappreciated that regardless of whether the housing of a sphericalbearing arrangement made according to a method embodying the presentinvention comprises the housing 2, 12, 16, 17 of any of FIGS. 1 to 6,the benefits of the present invention will still be realised. The formof the bearing housings shown in FIGS. 1 to 6 are not to be seen aslimiting.

When used in this specification and claims, the terms “comprises” and“comprising” and variations thereof mean that the specified features,steps or integers are included. The terms are not to be interpreted toexclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the followingclaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaining the disclosed result, as appropriate,may, separately, or in any combination of such features, be utilised forrealising the invention in diverse forms thereof.

1. A method of manufacturing a spherical bearing arrangement, the methodcomprising: providing a ball and a cast bearing housing; elevating theductility of the cast bearing housing; and swaging the housing onto theball whilst the ductility is elevated, the ductility lowering afterswaging.
 2. A method according to claim 1, further comprising:performing at least one machining operation on the cast housing prior toswaging thereof.
 3. A method according to claim 1, further comprising:performing at least one machining operation on the resultant sphericalbearing arrangement.
 4. A method according to claim 1, wherein theelevation of the ductility is performed by heating the housing.
 5. Amethod according to claim 1, wherein the ductility is lowered afterswaging by cooling the housing.
 6. A method according to claim 1,wherein the ductility of the housing prior to elevation is less than10%.
 7. A method according to claim 1, wherein the ductility of thehousing prior to elevation is less than or equal to substantially 9%. 8.A method according to claim 1, wherein the ductility of the housingprior to elevation is less than or equal to substantially 8%.
 9. Amethod according to claim 1, wherein the ductility of the housing priorto elevation is less than or equal to substantially 7%.
 10. A methodaccording claim 1, wherein the elevated ductility is at least 10%.
 11. Amethod according to claim 1, wherein the elevated ductility is at leastsubstantially 11%.
 12. A method according to claim 1, wherein theelevated ductility is at least substantially 12%.
 13. A method accordingto claim 1, wherein the elevation of the ductility is performed byproviding the housing at a predetermined temperature.
 14. A methodaccording to claim 13, wherein the predetermined temperature is at leastsubstantially 80° C.
 15. A method according claim 13, wherein thepredetermined temperature is at least substantially 90° C.
 16. A methodaccording claim 13, wherein the predetermined temperature is at leastsubstantially 100° C.
 17. A method according claim 13, wherein thepredetermined temperature is at least substantially 110° C.
 18. A methodaccording claim 13, wherein the predetermined temperature is at leastsubstantially 120° C.
 19. A method according to claim 1, wherein thelowered ductility of the housing is at least substantially equal to theductility of the housing before elevation.
 20. A method according toclaim 19, wherein the lowered ductility of the housing is substantiallygreater than the ductility of the housing before the elevation.
 21. Amethod according to claim 1, wherein the material of the bearing housingcomprises metal.
 22. A method according to claim 21, wherein the metalis zinc or zinc alloy.
 23. A spherical bearing arrangement manufacturedaccording to the method of claim
 1. 24. A spherical bearing arrangement,comprising a cast bearing housing swaged onto a ball, wherein theductility of the housing is elevated during swaging and lowered afterswaging.
 25. A rod end bearing comprising the spherical bearingarrangement according to claim 24.